Aquaculture refers to practice of producing seeds of aquatic animals or plants and growing or cultivating the produced seeds in a given water area in order to use adult animals or plants for food or for other purposes. Sea cucumber cultivation may include seed scattering type cultivation of scattering sea cucumber seeds over a suitable cultivation area, embankment type cultivation, hanging type cultivation, land-based aquatic plant type cultivation, etc.
In seed scattering type cultivation, sea cucumber seeds are scattered and grown over a sea area abounding in seaweeds and adult sea cucumbers are picked or harvested by divers. In hanging type cultivation, infant sea cucumbers are accommodated and artificially fed within wicker baskets or cylindrical baskets which are suspended in the sea. In embankment type cultivation, banks are formed using stones so that seawater flows freely through gaps between the stones to maintain good water quality, and infant sea cucumbers within the banks are fed with artificial or natural foods. In the land-based aquatic plant type cultivation, using pieces of polycarbonate plates and/or mesh type sacks, infant sea cucumbers are cultivated together with abalones therein.
FIG. 1 is a perspective view of an aquatic plant for cultivation of sea cucumbers employed in conventional land-based circulation aquatic plant type cultivation.
Referring to FIG. 1, a land-based circulation aquatic plant 1 has an exposed top face with a rectangular partitioned form using a concrete material. The plant 1 includes a seawater supply device for supplying the seawater from the sea to the plant. A plurality of strings is disposed across the exposed top face and a plurality of mesh type sacks are hung from the strings so as to be in contact with a bottom of the plant. In some cases, sea cucumbers are cultivated together with abalones.
FIG. 2 is a perspective view of a fish cultivation aquatic plant used in conventional land-based aquatic plant type cultivation.
Referring to FIG. 2, a conventional fish cultivation aquatic plant 2 has an exposed top face with a circular or square shape. The plant 2 includes a discharge pipe through which seawater containing excreta of fish, food residues and/or containments such as organic or inorganic materials is discharged to the coastal area. Such land-based aquatic plant cultivation has become commonplace.
A sea cucumber belonging to echinodermata can not swim unlike fish but crawls on the surface, and is a nocturnal animal. Therefore, sea cucumbers crawl in an attached manner onto bottom and side surfaces of the conventional sea cucumber or fish cultivation plant. However, since the bottom and side surfaces of the conventional sea cucumber or fish cultivation plant are made of hard concrete or FRP (Fiber Reinforced Plastic), dissolved oxygen may not be supplied to sea cucumbers through the bottom and side surfaces thereof. Although oxygen may be artificially supplied into the plant, the oxygen may not reach sea cucumbers well due to fast floating of oxygen in water.
Moreover, a seawater discharge hole is located at a center of the cultivation plant and thus seawater is discharged at lower or high flow rates. Therefore, sea cucumbers seeds and food may be lost. Otherwise, food settled on the bottom becomes corrupted as time goes by, generating harmful gases. Such harmful gases may suffocate sea cucumbers or the corrupted food may come into contact with the skins of sea cucumbers, thus killing the sea cucumbers. Since sea cucumbers are nocturnal animals and light is not screened from the exposed top face, resulting in a small dark space, a living area of sea cucumbers is small and a population density of the cultivated sea cucumbers is low and sea cucumbers are not raised with good health due to the narrow movement area. In addition to these problems, sea pollution may increase due to the corrupted food residues and weights of sea cucumbers may reduce especially within hot seawater in midsummer.
As for the seed scattering type cultivation, sea cucumbers seeds are scattered randomly over a given sea farm and are naturally raised for a certain period until adult sea cucumbers are to be picked or harvested for sale. Therefore, seed scattering type cultivation may be cost-efficient in terms of cultivation but may be labor-intensive in terms of harvesting. In seed scattering type cultivation, not only is it difficult to harvest the scattered sea cucumbers but also survival and collection rates of sea cucumbers may be low because of harmful organisms.
As for hanging type cultivation using wicker baskets or cylindrical baskets, there may occur the following problems: loss of a cultivator due to unique physical nature of the sea, that is, high waves for example from typhoons; death of sea cucumbers due to red tides; weight reduction of sea cucumbers due to high temperature seawater or irregular feeding; increasing effect of stress on sea cucumbers resulting from movement of a cultivator in feeding; and low population density of the cultivated sea cucumber due to a small area of the cultivator.
As for embankment type cultivation, there may occur the following problems: weight reduction of sea cucumbers due to high temperature seawater in the summer or frozen seawater in the winter; increase of sea pollution due to food residues; increase of food price for sea cucumbers; and harmful effects on other sea farms due to interruption of seawater flow.